1. Field of the Invention
The present invention relates to a head actuator mechanism used for a disc apparatus such as a hard disc apparatus using a disc as an information storage medium.
2. Related Art of the Invention
Magnetic disc apparatuses such as hard disc and floppy disc apparatuses conventionally use the same magnetic head to write and read data. On the contrary, attention is being paid to the application to magnetic disc apparatuses of very sensitive read-only heads using a magnetic-resistance effect element (MR elements), including so-called magnetic-resistance magnetic heads. Of course, the use of such a read-only head requires a separate write-only magnetic head to be provided.
FIG. 40 shows an example of such a magnetic head formed by integrating a write and a read elements as a thin-film structure. This is a head based on a "piggyback" method which is constituted by laminating an MR element 22 acting as a read element and a lead conductor 23 connected to the MR element, via an insulating layer 21 on a head slider 20, and laminating thereon via an insulating layer 24 a write element comprising a lower and an upper cores 25 and 26 and a write gap 27 and a coil conductor 28 provided between the cores. The magnetic head is disposed so as to be opposed to the magnetic disc 29 as shown in the figure.
Currently, instead of the linear motor method, the rotary actuator method enabling the magnetic head to be moved at a high speed using a small apparatus is often used as a method for driving the magnetic head in the magnetic disc apparatus. As shown in FIG. 41, this method uses a rotating shaft 32 as a support point to rotate an arm 31 with a magnetic head 30 attached to its tip in order to move the magnetic head 30 in the radial direction between the inner and outer circumferences of the magnetic disc 29 for seeking. According to this method, the relative angle between the track direction and the magnetic head 30 is not constant in each track. In other words, the azimuth angle (between the gap direction and track width direction of the magnetic head 30) of the magnetic head 30 varies with the track. If the magnetic head 30 is used for both writes and reads, no problem occurs even if the relative angle between the track direction and the magnetic head varies with the track.
If, however, the magnetic head 30 comprises the individually configured write and read elements arranged on the same slider in parallel as shown in FIG. 40 and the relative angle varies with the track, the trace position may be different for a write element 40 and a read element 41 laminated as shown in FIG. 42. FIG. 42 shows a difference in the trace position for the write and read elements 40 and 41 caused by the difference in the relative angle between the track direction and the magnetic head. As shown in FIG. 42(a), when the relative angle between the track direction and the write and read elements 40 and 41 is 90.degree. (corresponding to the azimuth angle of 0.degree.), the write and read elements 40 and 41 trace the same position (shown by arrow 43) in the same track 42. On the contrary, if the relative angle between the track direction and the write and read elements 40 and 41 becomes different from 90.degree., for example, the track 44 is displaced toward the outer circumference relative to the state in FIG. 42(a), as shown in FIG. 42(b), the write element 40 traces the position shown by arrow 45, while the read element 41 the position shown by arrow 46 which is slightly closer to the inner circumference, resulting in a difference in traced track 44 position (this is called a "track offset") between writes and reads. Consequently, the read output from the read element 41 decreases in such a way as to correspond to the rate of track offset relative to the track width. The decrease in read output caused by the track offset increases with decreasing track width due to the increasing density of the track, causing an increase in error rate.
As described above, when a magnetic head comprising a write and a read elements that are individually configured is driven by a rotary actuator as in the prior art, the track offset may occur between writes and reads to reduce the read output.
This invention is provided in view of this point, and its object is to provide a magnetic disc apparatus that prevents the track offset between writes and reads even if a magnetic head comprising a write and a read elements that are individually configured is driven by a rotary actuator.